The present invention relates to methods and compositions for treating subterranean formations with swellable lost circulation materials.
Hydrocarbon producing wells are typically formed by drilling a wellbore into a subterranean formation. A drilling fluid is circulated through a drill bit within the wellbore as the wellbore is being drilled. The drilling fluid is produced back to the surface of the wellbore with drilling cuttings for removal from the wellbore. The drilling fluid maintains a specific, balanced hydrostatic pressure within the wellbore, permitting all or most of the drilling fluid to be produced back to the surface. However, the hydrostatic pressure of the drilling fluid may be compromised if the drill bit encounters certain unfavorable subterranean zones, such as low pressure zones caused by natural fissures, fractures, vugs, or caverns, for example. Similarly, if the drill bit encounters high pressure zones, crossflows or an underground blow-out may occur. The compromised hydrostatic pressure of the drilling fluid causes a reduction of drilling fluid volume returning to the surface, termed “lost circulation.” In addition to drilling fluids, other operational treatment fluids, such as fracturing fluid, may be lost to the subterranean formation due to fluid loss. The term “lost circulation” refers to loss of a drilling fluid, while the term “fluid loss” is a more general term that refers to the loss of any type of fluid into the formation. As a result, the service provided by the treatment fluid is often more difficult to achieve or suboptimal.
The consequences of lost circulation or fluid loss can be economically and environmentally devastating, ranging from minor volume loss of treatment fluids, to delayed drilling and production operations, to an underground well blow-out. Therefore, the occurrence of lost circulation or fluid loss during hydrocarbon well operations typically requires immediate remedial steps. Remediation often involves introducing a composition into the wellbore to seal unfavorable subterranean zones and prevent leakoff of the treatment fluids within the formation to unfavorable zones (“fluid loss zones”). Such compositions are generally referred to as “fluid loss control materials” or “FLCM.”
Typical FLCMs are roughly spherical, having a sphericity of about 0.7 to about 1, and formed from cementitious material, flexible polymeric material, or naturally occurring materials (e.g., nut shell pieces or cellulosic materials), for example. In some cases, multiple FLCM types are mixed and used together to treat fluid loss in order to gain the functional benefit of each type.
Traditional FLCMs, however, may only partially seal a fluid loss zone, particularly when the fluid loss zone is a large cavernous or vugular zone. Multiple factors may affect the success of a fluid loss control operation, including, but not limited to, the wellbore size, the wellbore depth, the types of treatment fluids used, the drill bit nozzle size, and the FLCM shape and size. For instance, a particular sized and shaped FLCM may be required to adequately treat a formation, but is of such a size and shape that it interferes with the pumpability of the operational fluid into the wellbore, causing potential damage to drilling equipment and delay. Additionally, traditional FLCMs may form insufficient contact among one another to withstand stresses within the subterranean formation (e.g., the stresses of formation itself, the fluid loss zone, other FLCM particulates, the stress of flowing treatment fluids, and the like). Traditional FLCMs may also fail to interact with one another to sufficiently prevent treatment fluids from leaking-off into a formation due to the presence of interstitial spaces between aggregated individual FLCMs. This may be particularly so if the FLCMs are of similar shapes and sizes. Moreover, the presence of such interstitial spaces may result in a widening of the interstitial spaces as fluid flows through, thereby compounding the fluid loss problem. Accordingly, an ongoing need exists for methods and compositions of blocking the flow of fluid through fluid loss zones in a subterranean formation.